Why don’t Walk-in Coolers have filters?

The evaporators on a walk-in cooler or freezer are specifically made not to have filters. The metering devices/TXVs ( I think of them as the carburetor of the refrigerant world) that feed the evaporators, monitor and adjust the flow of refrigerant into them depending on the superheat at the tailpipe of the evaporator. If this airflow were to change at all, so would the refrigerant flow control done by the TXVs. Because the filters would cause a higher static pressure increases and decreases, the TXVs would go wide open to shut down back to wide open causing flooding and starvation both. This would in turn causes the compressor to refrigerant flood which could break valves or wash the oil out of the crankcase. On the other hand, when the TXV is starving the evaporator, it is also starving the compressor, causing overheating since the compressor is refrigerant cooled.

The proper way to handle this is to do periodic cleaning on these evaporators. Make sure to call a trained technician that is used to dealing with the very thin and easily damaged aluminum fins these evaporators have and enjoy the long life of your walk-in cooler.